Photolytically cleavable, N-acylated sterically hindered amines

ABSTRACT

Sterically hindered cyclic amines which are substituted by a photoactivatable acyl group at the basic nitrogen atom can be deacylated by irradiation with UV light. This is advantageous if the basicity of the amines proves troublesome during application. Examples of such photoactivatable acyl groups are phenylglyoxyl, phenylacetyl or naphthylacetyl groups.

The present invention relates to photolytically cleavable, N-acylatedsterically hindered amines and to the use thereof for stabilisingpolymers against light-induced damage, in particular for stabilisingacid curable resins.

It is known that sterically hindered amines are effective lightstabilisers for polymers. Particular importance attaches to the lightprotection of varnishes for producing industrial finishes of which along service life is required, e.g. automotive finishes or machinefinishes. Acid-catalysed stoving varnishes are often used for obtainingsuch finishes. The addition of acid curing catalysts as well as aminelight stabilisers to such varnishes before curing may result in unwantedinteractions of both these components. This problem can be overcome byusing N-acylated piperidines as "amine light stabilisers" in accordancewith the teaching of European patent application No. EP-A-52 073. Thesecompounds are no longer basic and thus do not give rise to interactionswith acid catalysts. However, the light protective action of theN-acylated piperidines is usually inferior to that of the analogousN-unsubstituted or N-alkylated piperidines. The problem was therefore toprovide light stabilisers which do not undergo interaction with the acidcatalyst and which induce in the cured varnish as good alight-stabilising effect as the N-unsubstituted or N-alkylated aminelight stabilisers. The same consideration also applies to acid curableresins, aside from their utility as varnishes.

It has been found that this problem can be solved by using N-acylated,sterically hindered amines as light stabilisers, which amines can becleaved by photolysis and converted into N-unsubstituted amine lightstabilisers after curing the resin by irradiation. These photolyticallycurable amine light stabilisers are so far not known in the art andtherefore had to be developed specially for this purpose.

Accordingly, the invention relates to compounds of formula I ##STR1##wherein m is 1, 2 or 3,

A is a R¹ --CO-- or R² --CH₂ -- group, wherein

R¹ is phenyl or phenyl which is substituted by halogen, C₁ -C₁₂ -alkyl,C₁ -C₄ alkoxy or hydroxy, or is naphthyl, C₁ -C₁₂ alkoxy, cyclohexyloxy,phenoxy or benzyloxy and, if m=1, may also be a radical B,

R² is halogen, phenyl, naphthyl, --CN, --P(O)(OR³)₂, --CH₃ CO-- or--OR⁴, wherein

R³ is C₁ -C₄ alkyl or phenyl, and

R⁴ is phenyl or phenyl which is substituted by halogen or C₁ -C₄ alkyl,and

B is a radical of valency m of a sterically hindered cyclic amine whichis attached to the A--CO-- radical through the sterically hinderednitrogen atom.

The cyclic amine radical B can be a 5-, 6- or 7-membered ring which mayalso contain other hetero atoms in addition to the basic nitrogen atom.However, the radical B is not an aromatic heterocyclic radical. Inparticular, where m=1, B may be a radical of formula ##STR2## wherein R⁵is hydrogen, --OR⁸, ##STR3## --N(R¹⁰ R¹¹), R⁶ is --OH or --OR¹² and R⁷is --OR¹², --CN, --COOR¹³ or --CONH₂, or R⁶ and R⁷ together are the oxoradical (═O), or R⁶ and R⁷, together with the C-atom to which they areattached, form a heterocyclic spiro ring which may be a2-spiro-1,3-dioxolane, 2-spiro-1,3-dioxane, 5-spiro-1,3-oxazolidine,2-spiro-1,3-oxazolidine or 5-spiro-1,3-imidazolidine ring and which maybe substituted by one or more identical or different members selectedfrom alkyl, substituted alkyl, alkylene and/or the oxo radical,

R⁸ is C₁ -C₁₂ alkyl, benzyl, allyl or 2-cyanoethyl,

R⁹ is C₁ -C₁₈ alkyl, C₂ -C₁₂ alkenyl, C₅ -C₈ cycloalkyl, phenyl orphenyl which is substituted by halogen, C₁ -C₁₂ alkyl, C₁ -C₄ alkoxyand/or hydroxyl, or is C₇ -C₁₂ phenylalkyl, C₁ -C₄ alkoxy or phenoxy,

R¹⁰ is C₁ -C₁₂ alkyl, cyclohexyl, phenyl, naphthyl, or phenyl which issubstituted by C₁ -C₄ alkyl,

R¹¹ is C₂ -C₁₂ alkanoyl, C₃ -C₈ alkenoyl, benzoyl or a group of theformula ##STR4## wherein R¹⁴ and R¹⁵ are each independently of the otherC₁ -C₈ alkoxy, phenoxy, or a group --N(R¹⁰)(R¹⁶), in which R¹⁶ ishydrogen or C₁ -C₁₂ alkyl,

R¹² is C₁ -C₁₂ alkyl and R¹³ is C₁ -C₄ alkyl, and

Y is hydrogen, C₁ -C₁₂ alkyl, allyl or benzyl.

Where m is 2, B may in particular be a divalent radical selected from:##STR5## wherein Z is --O--, --NH-- or --NR¹⁰,

R¹⁷ is a divalent aliphatic, cycloaliphatic or aromatic radical of 1 to20 carbon atoms or a radical --NH--R¹⁹ --NH--,

R¹⁸ is a divalent aliphatic or cycloaliphatic or aromatic radical of 2to 12 carbon atoms,

R¹⁹ is a divalent aliphatic, cycloaliphatic or aromatic radical of 2 to16 carbon atoms, and

R¹⁰ and R¹⁴ are as previously defined.

Where m=3, B may be in particular a trivalent radical of formula##STR6## wherein R²⁰ is a trivalent aliphatic radical of 3 to 8 carbonatoms or a trivalent aromatic radical of 6 to 10 carbon atoms, R²¹ is a1,3,5-triazin-2,4,6-triyl radical, and Z is as previously defined.

Substituents defined above as alkyl may be unbranched or branched alkyl.R³ and R¹³ as C₁ -C₄ alkyl are methyl, ethyl, n-propyl, isopropyl,n-butyl, sec-butyl, isobutyl or tert-butyl. R⁸, R¹⁰, R¹², R¹⁶ and Y asC₁ -C₁₂ alkyl may be pentyl, n-hexyl, 2-ethylbutyl, n-octyl,2-ethyl-n-hexyl, n-nonyl, isodecyl or n-dodecyl. R⁹ as C₁ -C¹⁸ alkyl maybe tetradecyl, hexadecyl or octadecyl.

R⁹ as C₂ -C₁₂ alkyl may be vinyl, allyl, 2-propenyl, methallyl,2-buten-1-yl, 2-buten-2-yl, 2-hexen-1-yl, 2-octen-1-yl or10-un-decen-1-yl.

R⁹ as C₅ -C₆ cycloalkyl may be cyclopentyl, cyclohexyl, methylcyclohexylor cyclooctyl. R⁹ as C₇ -C₁₂ phenylalkyl may be benzyl, 1- or2-phenylethyl or 3-phenylpropyl.

R¹, R⁴ and R⁹ as substituted phenyl radicals may be 4-chlorophenyl,3-bromophenyl, 2-fluorophenyl, 4-methylphenyl, 2,4-dimethylphenyl,4-tert-butylphenyl, 3-methoxyphenyl or 4-ethoxyphenyl. R¹ and R⁹ mayalso be 4-octylphenyl, 4-dodecylphenyl, 4-hydroxyphenyl,2-methyl-4-hydroxyphenyl or 3,5-di-(tert-butyl)-4-hydroxyphenyl.

R⁹, R¹⁴ and R¹⁵ as alkoxy radicals may be methoxy, ethoxy or butoxy. R¹⁴and R¹⁵ may also be hexyloxy, octyloxy, decyloxy or dodecyloxy.

R¹¹ as alkanoyl or alkenoyl may be acetyl, propionyl, butyroyl,hexanoyl, octanoyl, lauroyl, acryloyl, methacryloyl or crotonoyl.

R¹⁷ as a divalent aliphatic, cycloaliphatic or aromatic radical may bemethylene, 1,2-ethylene or C₃ -C₂₀ polymethylene; or branched C₃ -C₂₀alkylene such as 1,2-propylene or trimethyltetramethylene; or C₂ -C₁₀alkenylene such as vinylene or 2-buten-1,4-ylene; or cycloalkylene suchas 1,4-cyclohexylene or 1,3-cyclohexylene; or cycloalkane-dialkylenesuch as cyclohexane-1,4-dimethylene; or arylene such as 1,3- or1,4-phenylene, 1,4- or 1,5-naphthylene, 4,4'-diphenylene,diphenylmethane-4,4'-diyl or diphenyl oxide-4,4'-diyl; or aralkylenesuch as m- or p-xylene.

R¹⁸ as a divalent aliphatic, cycloaliphatic or aromatic radical ispreferably a radical of 2 to 8 carbon atoms. Examples of such radicalsare 1,2-ethylene, 1,2-propylene, 1,3-propylene, 1,2-butylene,1,4-butylene, hexamethylene, 1,4-cyclohexylene orcyclohexane-1,4-dimethylene.

R¹⁹ as a divalent aliphatic, cycloaliphatic or aromatic radical may bean unbranched or branched alkylene radical such as 1,2-ethylene,trimethylene, tetramethylene, hexamethylene, octamethylene,dodecamethylene, 2,2-dimethyltrimethylene or trimethyloctamethylene; ora cycloalkylene radical such as 1,4-cyclohexylene; orcycloalkanealkylene such as cyclohexane-1,4-dimethylene; or arylene suchas 1,3-phenylene, 4,4'-diphenylene, diphenylmethane-4,4'-diyl ordiphenyl oxide-4,4'-diyl; or arene-dialkylene such as m- or p-xylylene.

R²⁰ as a trivalent aliphatic or aromatic radical may bepropane-1,2,-3-triyl, butane-1,2,4-triyl, benzene-1,3,5-triyl,benzene-1,2,4-triyl or naphthalene-1,4,5-triyl.

Preferred compounds of formula I are those wherein A is a R¹ --CO-- orR² --CH₂ -- group, wherein R¹ is phenyl or phenyl which is substitutedby halogen, C₁ -C₁₂ alkyl or C₁ -C₄ alkoxy, or is unsubstitutednaphthyl, and R² is phenyl, naphthyl, --CN or CH₃ CO--.

Particularly preferred compounds of formula I are those wherein A is abenzoyl group or an α-naphthylmethyl group. Further preferred compoundsof formula I are those wherein m is 1 or 2 and B is a group of formulaeII, III or IV.

Where m=1 and A is B--CO, the compounds conform to the formulaB--CO--CO--B, wherein both radicals B are attached to the --CO groupthrough their sterically hindered nitrogen atoms.

The compounds of formula I can be prepared in principle from theN-unsubstituted amines (H)_(m) B by reaction with the correspondingcarboxylic acid chlorides A--COCl or anhydrides (A--CO)₂ O. Thecompounds B--CO--CO--B can be prepared by reaction of 2 moles of H--Bwith 1 mole of oxalyl chloride. The N-unsubstituted sterically hinderedcyclic amines are known compounds which have been described in a numberof patent specifications, for example U.S. Pat. Nos. 3,640,928,3,790,525 and 3,639,409.

Some of the acid chlorides A--COCl are known compounds or can beprepared from the corresponding carboxylic acids by known methods, forexample by reaction with thionyl chloride. Some of the anhydrides arealso known and can be prepared e.g. by the method described in J.Cabre-Castelvi et al., in Synthesis, 1981, 616.

Representative examples of individual compounds of formula I are listedbelow. In these compounds, ##STR7## denotes a2,2,6,6-tetramethylpiperidine radical Ph- is a phenyl radical andNaphth- is an α-naphthyl radical. ##STR8##

The compounds of formula I are intrinsically light stabilisers fororganic polymers and can be used for stabilising them without the needfor irradiation. To this end they are normally incorporated in thepolymers before these are processed to moulded articles. However, theycan also be added during the manufacture of the polymers. The followingclasses of polymer are examples of polymers which are sensitive to theaction of light and which can be stabilised by addition of the compoundsof this invention.

1. Polymers of mono- and diolefins, for example polyethylene(uncrosslinked or crosslinked), polypropylene, polyisobutylene,polybut-1-ene, polymethylpent-1-ene, polyisoprene or polybutadiene, andpolymers of cycloolefins, e.g. of cyclopentene or norbornene.

2. Mixtures of the polymers mentioned under (1), for example mixtures ofpolypropylene with polyethylene or with polyisobutylene.

3. Copolymers of mono- and diolefins with each other or with other vinylmonomers, for example ethylene/propylene copolymers, propylene/but-1-enecopolymers, propylene/isobutylene copolymers, ethylene/but-1-enecopolymers, propylene/butadiene copolymers, isobutylene/isoprenecopolymers, ethylene/alkylacrylate copolymers,ethylene/alkylmethacrylate copolymers, ethylene/vinyl acetatecopolymers, or ethylene/acrylic acid copolymers and salts thereof(isomers), as well as terpolymers of ethylene with propylene and a dienesuch as hexadiene, dicyclopentadiene or ethylidene norbornene.

4. Polystyrene, poly-(p-methylstyrene).

5. Copolymers of styrene or α-methylstyrene with dienes or acrylicderivatives, for example styrene/butadiene, styrene/acrylonitrile,styrene/alkylmethacrylate, styrene/acrylonitrile/methyl acrylate,mixtures of high impact strength obtained from styrene copolymers andanother polymer, for example a polyacrylate, a diene polymer or anethylene/propylene/diene terpolymer; and also block copolymers ofstyrene, for example styrene/butadiene/styrene,styrene/isoprene/styrene, styrene/ethylene/butylene/styrene, orstyrene/ethylene/propylene/styrene.

6. Graft copolymers of styrene, e.g. styrene with polybutadiene, styreneand acrylonitrile with polybutadiene, styrene and maleic anhydride withpolybutadiene, styrene and alkyl acrylates or alkyl methacrylates withpolybutadiene, styrene and acrylonitrile with ethylene/propylene/dieneterpolymers, styrene and acrylonitrile with polyalkylacrylates orpolyalkylmethacrylates, styrene and acrylonitrile withacrylate/butadiene copolymers, and mixtures thereof with the copolymerslisted under (5), known e.g. as ABS, MBS, ASA or AES polymers.

7. Halogen-containing polymers, e.g. polychloroprene, chlorinatedrubber, chlorinated or chlorosulfonated polyethylene, especiallypolymers of halogenated vinyl compounds, e.g. polyvinyl chloride,polyvinylidene chloride, polyvinyl fluoride, polyvinylidene fluoride andtheir copolymers such as vinyl chloride/vinylidene chloride, vinylchloride/vinyl acetate or vinylidene chloride/vinyl acetate polymers.

8. Polymers which are derived from α,β-unsaturated acids and theirderivatives, e.g. polyacrylates and polymethacrylates, polyacrylamidesand polyacrylonitriles.

9. Copolymers of the monomers listed in (8) with one another or withother unsaturated monomers, e.g. acrylonitrile/butadiene copolymers,acrylonitrile/alkylacrylate copolymers, acrylonitrile/vinyl halidecopolymers, or acrylontrile/alkylmethacrylate/butadiene terpolymers.

10. Polymers which are derived from unsaturated alcohols and amines ortheir acyl derivatives or acetals, e.g. polyvinyl alcohol, polyvinylacetate, polyvinyl stearate, polyvinyl benzoate, polyvinyl maleate,polyvinylbutyral, polyallyl phthalate, polyallyl melamine.

11. Homopolymers and copolymers of cyclic ethers such as polyethyleneglycols, polyethylene oxide, polypropylene oxide or their copolymerswith bisglycidyl ethers.

12. Polyacetals such as polyoxymethylene, and also thosepolyoxymethylenes which contain e.g. ethylene oxide as comonomer.

13. Polyphenyl oxides and polyphenyl sulfides and mixtures thereof withstyrene polymers.

14. Polyurethanes which are derived on the one hand from polyethers,polyesters and polybutadienes containing hydroxy end groups, and fromaliphatic or aromatic polyisocyanates on the other, as well as theirprecursors (polyisocyanates, polyols, prepolymers).

15. Polyamides and copolyamides which are derived from diamines anddicarboxylic acids and/or from aminocarboxylic acids or thecorresponding lactams, such as polyamide 4, polyamide 6, polyamide 66,polyamide 610, polyamide 11, polyamide 12,poly-2,4,4-trimethylhexamethyleneterephthalamide,poly-m-phenylene-isophthalamide, and their block copolymers withpolyethers, e.g. with polyethylene glycol, polypropylene glycol orpolytetramethylene glycol.

16. Polyureas, polyimides and polyamide-imides.

17. Polyesters which are derived from dicarboxylic acids and diolsand/or from hydroxycarboxylic acids or the corresponding lactones, e.g.polyethylene terephthalate, polybutylene, terephthalate,poly-1,4-dimethylolcyclohexane terephthalate, polyhydroxybenzoates, andalso block polyether esters which are derived from hydroxyl-terminatedpolyethers.

18. Polycarbonates.

19. Polysulfones, polyether sulfones and polyether ketones.

20. Crosslinked polymers which are derived from aldehydes on the onehand and from phenols, ureas and melamines on the other hand, e.g.phenol/formaldehyde resins, urea/formaldehyde resins andmelamine/formaldehyde resins.

21. Drying and non-drying alkyd resins.

22. Unsaturated polyester resins which are derived from copolyesters ofsaturated and unsaturated dicarboxylic acids with polyhydric alcoholsand from vinyl compounds as crosslinking agents, and also theirhalogen-containing modifications of low combustibility.

23. Crosslinkable acrylic resins which are derived from substitutedacrylic esters, e.g. from epoxy acrylates, urethane acrylates orpolyester acrylates.

24. Alkyd resins, polyester resins and acrylate resins which arecrosslinked with melamine resins, urea resins, polyisocyanates or epoxyresins.

25. Crosslinked epoxy resins which are derived from polyepoxides, e.g.bisglycidyl ethers, or from cycloaliphatic diepoxides.

26. Naturally occurring polymers such as cellulose, natural rubber andgelatin, and also chemically modified homologous derivatives thereofsuch as cellulose acetates, cellulose propionates and cellulosebutyrates, and cellulose ethers such as methylcellulose.

The amount of stabiliser added is in general 0.01 to 5% by weight,preferably 0.03 to 1.5% by weight and, most preferably, 0.2 to 0.6% byweight, based on the polymer to be stabilised.

The polymers may also contain other known stabilisers, for exampleantioxidants, light stabilisers, metal deactivators, phosphites,thiodicarboxylates, salts of higher fatty acids or other co-stabilisers.Other modifiers conventionally employed in plastics technology may alsobe added, for example antistats, plasticizers, lubricants, flameretardants, pigments, reinforcing agents or fillers.

If the stabilised polymers are in the form of thin layers, as they arein the case of sheets, filaments, varnishes and coatings, thestabilisers of formula I can be cleaved photochemically by irradiationwith shortwave light to form compounds which are unsubstituted at thesterically hindered nitrogen atom. Irradiation is preferably effectedwith UV light in the wavelength range from 250 to 400 nm. Suitable lightsources for the irradiation are for example medium-pressure,high-pressure and low-pressure mercury lamps as well as superactinicneon tubes. At the present time a whole range of suitable devices isavailable, especially for continuous irradiation, in which the materialto be irradiated is transported beneath the light source. The sameeffect is achieved when using the stabilised polymers in the open.

As mentioned at the outset, the photochemical conversion of theN-acylated stabiliser to an N-unsubstituted stabiliser is of particularimportance for stabilising acid-catalysed stoving varnishes by effectingirradiation after stoving.

Acid-curable varnishes are in particular those based on a binder thatcontains an amine resin, e.g. an etherified, esterified or otherwisemodified melamine resin, urea resin or guanidine resin. These varnishesare normally used in admixture with alkyd, polyester or acrylic resinswhich contain functional groups (e.g. --OH or --COOH groups) that arecrosslinked by reaction with the methylol groups of the amine resins.This crosslinking is catalysed by acids. Instead of the amine resin, thevarnish can also contain methylol derivatives of polycarboximides ortheir ethers or esters. Sulfonic acids are usually employed as acidcuring catalysts, but carboxylic acids or phosphonic acids or maskedsulfonic acids are also suitable.

Acid-catalysed stoving varnishes often contain mixtures of alkyd resins,polyester resins and acrylic resins with one another or with otherfilm-forming resins. Such film-forming resins may also beself-crosslinking, for example if they are modified by methylolamidegroups, in which case they do not require the addition of an amine resinor other crosslinking agent.

The stabilisers of this invention are incorporated in the varnishesbefore application, preferably by adding them to a solution of thestabiliser in an organic solvent. The stoving of the varnish is usuallyeffected in the temperature range from 100°-200° C. During stoving, thestabiliser must not volatilise and decompose. Not until the subsequentirradiation of the cured varnish coating does the photochemical cleavageof the stabilise occur.

For many finishes, especially automotive finishes, the two-coat methodis employed at the present time. This method comprises applying firstthe pigmented varnish and then the clear varnish to the undercoat. Thelight stabiliser can be added to the clear varnish as well as to thepigmented varnish or to both coatings.

To obtain maximum light-resistance, the concurrent use of otherconventional light stabilisers, e.g. UV absorbers or organic nickelcompounds, can be advantageous. The concurrent use of UV absorbers ofthe 2-hydroxybenzophenone, 2-(2-hydroxyophenyl)benztriazole or oxanilidetype, which may have a synergistic effect, is especially useful.Examples of such compounds are:2-(2-hydroxy-3,5-di-tert-amylphenyl)benztriazole,2-(2-hydroxy-5-tert-octylphenyl)benztriazole,2-(2-hydroxy-3,5-di-tert-octylphenyl)benztriazole,2,4-dihydroxybenzophenone, 2-hydroxy-4-octyloxybenzophenone,2-hydroxy-5-dodecyloxybenzophenone,2-ethyl-2-ethoxy-4'-tert-butyloxalanilide or2-ethyl-2'-ethoxyoxalanilide.

When using such combinations, the sum of all light stabilisers is 0.2 to5% by weight, preferably 0.5 to 2% by weight, based on the film-formingresin.

Further modifiers which may be present in the varnish are antioxidants,for example of the sterically hindered phenol derivative type,phosphorus compounds such as phosphites or phosphonites, plasticisers,levelling agents, thickeners, dispersants or bonding agents.

The following Examples illustrate the preparation of the compounds ofthis invention and the use thereof as stabilisers.

EXAMPLE 1

(a) 1 ml of piperidine is added to 30 g (0.2 mole) of phenylglyoxylicacid and 18.9 ml (0.26 mole) of thionyl chloride are added dropwise,with stirring, under nitrogen such that the temperature of the reactionmixture is 25°-30° C. The reaction mixture is then stirred for 24 hoursat 35°-40° C. and concentrated by evaporation at a maximum temperatureof 40° C. under vacuum. The residual crude phenylglyoxylyl chloride is ayellow oil containing an insignificant amount of powdery deposit. Thiscrude product is used without further purification for the subsequentreactions.

(b) 24.1 g (0.1 mole) of 4-hexyloxy-2,2,6,6-tetramethylpiperidine aredissolved in 100 ml of absolute methylene chloride. To this solution areadded 15.2 g (0.15 mole) of absolute triethylamine and the wholesolution is cooled to -10° C. At this temperature a solution of 16.8 g(0.1 mole) of phenylglyoxylyl chloride in 100 ml of methylene chlorideis slowly added dropwise. When this addition is complete, the reactionmixture is allowed to warm to room temperature and stirred for about 4hours. Precipitated hydrochloride is removed by filtration and thesolution is clarified by filtration over a small amount of silica geland concentrated by evaporation, affording 28.4 g of1-(4-hexyloxy-2,2,6,6-tetramethylpiperidino)-2-phenylethane-1,2-dione asa yellow oil (stabiliser 1).

    ______________________________________                                        Analysis: theory                                                                        C =      73.96%  found   C =  73.77%                                          H =      9.44%           H =  9.20%                                           N =      3.75%           N =  3.25%                                 ______________________________________                                    

Analogous reaction of phenylglyoxylyl chloride with the correspondingcyclic amines gives the following compounds:

3-dodecyl-8-(2-phenylethane-1,2-dion-1-yl)-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione(stabiliser 2);

    ______________________________________                                        Analysis: theory                                                                        C =      70.82%  found   C =  70.46%                                          H =      9.02%           H =  8.82%                                           N =      7.99%           N =  7.96%                                 ______________________________________                                    

3-dodecyl-1,8-bis(2-phenylethane-1,2-dion-1-yl)-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione(stabiliser 3);

    ______________________________________                                        Analysis: theory                                                                        C =      71.20%  found   C =  68.82%                                          H =      7.81%           H =  7.72%                                           N =      6.38%           N =  6.19%                                 ______________________________________                                    

bis-[1-(2-phenylethane-1,2-dion-1-yl)-2,2,6,6-tetramethylpiperidin-4-yl]adipate,m.p. 135°-137° C. (stabiliser 4);

1-(4-benzoyloxy-2,2,6,6-tetramethylpiperidino)-2-phenylethane-1,2-dione,m.p. 122°-124° C. (stabiliser 5);

1-(4-dodecyloxy-2,2,6,6-tetramethyl(piperidino)-2-phenylethane-1,2-dionein the form of a yellow oil (stabiliser 6);

    ______________________________________                                        Analysis: theory                                                                        C =      76.10%  found   C =  75.78%                                          H =      10.35%          H =  10.18%                                          N =      3.06%           N =  2.93%                                 ______________________________________                                    

EXAMPLE 2

Analogous reaction of ethyl oxalyl chloride (C₂ H₅ OCOCOCl) with thecorresponding cyclic amines gives the following compounds:

ethyl 2-[4-hexyloxy-2,2,6,6-tetramethylpiperidino]-2-oxoacetate(stabiliser 7);

    ______________________________________                                        Analysis: theory                                                                        C =      66.82%  found   C =  66.80%                                          H =      10.33%          H =  10.32%                                          N =      4.10%           N =  4.07%                                 ______________________________________                                    

3-dodecyl-8-(ethoxyoxalyl)-7,7,9,9-tetramethyl-1,3,8-triazaspiro[4.5]decane-2,4-dione(stabiliser 8) of formula ##STR9## m.p. 81°-82° C. ethyl2-(4-benzoyloxy-2,2,6,6-tetramethylpiperidino)-2-oxoacetate (stabiliser9);

    ______________________________________                                        Analysis: theory                                                                        C =      66.46%  found   C =  66.33%                                          H =      7.53%           H =  7.56%                                           N =      3.88%           N =  3.90%                                 ______________________________________                                    

cyclohexanespiro-2'-[1-(ethoxyoxalyl)-1,3-diazolidin-4-one]-5'-spirocyclohexaneof formula ##STR10## (stabiliser 10), m.p. 211°-213° C.bis[1-(ethoxyoxalyl)-2,2,6,6-tetramethylpiperidin-4-yl]adipate(stabiliser 11), m.p. 74°-76° C.

Analogous reaction with oxalyl chloride gives the following compounds:

oxalyl di(4-benzoyl-2,2,6,6-tetramethyl)piperidide ##STR11## (stabiliser12), m.p. 211°-214° C.1,1'-oxalyl-bis(2,2-pentamethylene-5,5-pentamethylene-1,3-diazolidin-4-one##STR12## (stabiliser 13), m.p. 192°-193° C.

EXAMPLE 3

A 750 ml sulfonating flask is charged with 49.7 g (0.19 mole) of4-benzoyloxy-2,2,6,6-tetramethylpiperidine and 25.4 g (0.1 mole) ofphenylacetic anhydride. The mixture is heated under nitrogen to 150° C.and the resultant orange melt is stirred for 6 hours at thistemperature. After this time, no more starting material can be detectedin a thin-layer chromatogram (in ethyl acetate as eluant). The melt isallowed to cool and then dissolved in ethyl acetate. The solution ispurified through a column of silica gel and concentrated by evaporation,affording a yellow resinous product (stabiliser 14) of formula ##STR13##

    ______________________________________                                        Analysis: theory                                                                        C =      75.96%  found   C =  75.75%                                          H =      7.70%           H =  7.56%                                           N =      3.69%           N =  3.17%                                 ______________________________________                                    

EXAMPLE 4

A two-layer metallic varnish is aplied to aluminium sheets. Theundercoat (20 μm) consists of an aluminum-pigmented varnish based on apolyester/cellulose acetobutyrate/melamine resin mixture. A clearvarnish (40 μm) based on a hydroxylated acrylic resin (Macrynal® SM 510N, ex Hoechst AG) and a polyisocyanate (Desmodur® N 75, ex Bayer AG) isapplied as topcoat. A solution of a stabiliser listed in Table 1 in a1:1 mixture of ethylene glycol/xylene is added to the clear varnish. Forcuring, the samples are heated to 80° C. for 45 minutes.

The samples are subjected to solar radiation in Florida (5° south) andthe surface gloss is measured at 6 month intervals in accordance withASTM Test Method D 523. An unstabilised sample of the same varnishserves as comparison.

                  TABLE 1                                                         ______________________________________                                                20° Gloss (%) after                                            Stabiliser                                                                              0     6        12  18     24  months                                ______________________________________                                        none      96    84       81  59     43                                        1% of 2   96    87       84  78     73                                        2% of 2   96    84       84  80     79                                        2% of 3   96    87       87  81     77                                        ______________________________________                                    

EXAMPLE 5

Samples are prepared using a two-layer metallic stoving varnishcomprising an undercoat (20 μm) of an aluminium-pigmentedpolyester/cellulose acetobutyrate/melamine resin varnish and a topcoatof a clear varnish (40 μm) based on a thermosetting acrylic resin(Viacryl® VC 373, ex Vianova) and a melamine resin (Maprenal® MF 590, exHoechst AG) as crosslinking agent. A stabiliser listed in Table 2 isadded to the acrylic resin. The samples are stoved for 30 minutes at130° C.

The samples are exposed in a Xenotest 1200 weathering device and the 20°gloss is measured at intervals of 800 hours in accordance with DIN 67530. The results are reported in Table 2.

                  TABLE 2                                                         ______________________________________                                        20° Gloss (%) after                                                    Stabiliser                                                                           0       800    1600   2400 3200   4000 h                               ______________________________________                                        none   81      53     26     20   --     --                                   1% of 5                                                                              87      65     52     35   23     19                                   1% of 6                                                                              88      77     55     42   31     26                                   ______________________________________                                    

Noticeable cracks occur in the samples without stabiliser after 2800hours exposure to weathering, whereas cracks do not appear in thestabilised samples until after 5200 hours exposure.

What is claimed is:
 1. A compound of formula I ##STR14## wherein m is 1,2 or 3,A is a R¹ --CO-- or R² --CH₂ -- group, wherein R¹ is phenyl orphenyl which is substituted by halogen, C₁ -C₁₂ alkyl, C₁ -C₄ alkoxy orhydroxy, or is naphthyl.[., C₁ -C₁₂ alkoxy, cyclohexyloxy, phenoxy orbenzyloxy.]. and, if m=1, may also be a radical B, R² is --CN,--P(O)(OR³)₂, CH₃ CO-- or OR⁴, wherein R³ is C₁ -C₄ alkyl or phenyl, andR⁴ is phenyl or phenyl which is substituted by halogen or C₁ -C₄ alkyl,and when m is 1, B is a radical corresponding to the formulae ##STR15##wherein R⁵ is hydrogen, --OR⁸, ##STR16## --N(R¹⁰ R¹¹), R⁶ is --OH or--OR¹² and R⁷ is --OR¹², --CN, --COOR¹³ or --CONH₂, or R⁶ and R⁷together are the oxo radical (═O), or R⁶ and R⁷, together with theC-atom to which they are attached, form an unsubstituted2-spiro-1,3-dioxolane, 2-spiro-1,3-dioxane, 5-spiro-1,3-oxazolidine,2-spiro-1,3-oxazolidine or 5-spiro-1,3-imidazolidine ring or said ringsubstituted by one or more identical or different members selected fromC₁ -C₁₂ alkyl or the oxo radical, R⁸ is C₁ -C₁₂ alkyl, benzyl, allyl or2-cyanoethyl, R⁹ is C₁ -C₁₈ alkyl, C₂ -C₁₂ alkenyl, C₅ -C₈ cycloalkyl,phenyl or phenyl which is substituted by halogen, C₁ -C₁₂ alkyl, C₁ -C₄alkoxy or hydroxyl, or is C₇ -C₁₂ phenylalkyl, C₁ -C₄ alkoxy or phenoxy,R¹⁰ is C₁ -C₁₂ alkyl, cyclohexyl, phenyl, naphthyl, or phenyl which issubstituted by C₁ -C₄ alkyl, R¹¹ is C₂ -C₁₂ alkanoyl, C₃ -C₈ alkenoyl,benzoyl or a group of the formula ##STR17## wherein R¹⁴ and R¹⁵ are eachindependently of the other C₁ -C₈ alkoxy, phenoxy, or a group--N(R¹⁰)(R¹⁶), in which R¹⁶ is hydrogen or C₁ -C₁₂ alkyl, R¹² is C₁ -C₁₂alkyl and R¹³ is C₁ -C₄ alkyl, and Y is hydrogen, C₁ -C₁₂ alkyl, allylor benzyl; when m is 2, B is a divalent radical corresponding to theformulae ##STR18## wherein Z is --O--, --NH-- or --NR¹⁰ --, R¹⁷ ismethylene, 1,2-ethylene, C₃ -C₂₀ polymethylene, or branched C₃ -C₂₀alkylene, C₂ -C₁₀ alkenylene, 1,4-cyclohexylene, 1,3-cyclohexylene,cyclohexane-1,4-dimethylene, 1,3- or 1,4-phenylene, 1,4- or1,5-naphthylene, 4,4'-diphenylene, diphenylmethane-4,4'-diyl, diphenyloxide-4,4'-diyl or m- or p-xylene, or a radical --NR--R¹⁹ --NH--, R¹⁸ is1,2-ethylene, 1,2-propylene, 1,3-propylene, 1,2-butylene, 1,4-butylene,hexamethylene, 1,4-cyclohexylene or cyclohexane-1,4-dimethylene, R¹⁹ is1,2-ethylene, trimethylene, tetramethylene, hexamethylene,oxtamethylene, dodecamethylene, 2,2-dimethyltrimethylene,trimethyloctamethylene, 1,4-cyclohexylene, cyclohexane-1,4-dimethylene,1,3-phenylene, 4,4'-diphenylene, diphenylmethane-4,4'-diyl, diphenyloxide-4,4'-diyl, or m- or p-xylylene, and R¹⁰ and R¹⁴ are as definedabove; and, when m is 3, B is a trivalent radical corresponding to theformulae ##STR19## wherein R²⁰ is propane-1,2,3-triyl,butane-1,2,4-triyl, benzene-1,3,5-triyl, benzene-1,2,4-triyl ornaphthalene-1,4,5-triyl, R²¹ is a 1,3,5-triazin-2,4-triyl radical and Zis as defined above.
 2. A compound according to claim 1 of formula I,wherein A is a R¹ --CO-- or R² --CH₂ --group, wherein R¹ is phenyl whichis substituted by halogen, C₁ -C₁₂ alkyl or C₁ -C₄ alkoxy, or isunsubstituted naphthyl, and R² is --CN or CH₃ CO--.
 3. A compoundaccording to claim 1 of formula I, wherein A is a benzoyl group.
 4. Acompound according to claim 1 of formula I, wherein m is 1 or 2 and B isa group of formula II, III or IV.
 5. A compound according to claim 4 ofthe formula ##STR20##